1. Field of the Invention
This invention relates to a skid control system for a vehicle having at least one wheel and a brake for the wheel, and more particularly to a skid control system in which, when the deceleration of the wheel exceeds the predetermined threshold deceleration, the brake pressure to the brake for the wheel is decreased with time, and when the acceleration of the wheel exceeds the predetermined threshold acceleration, the brake pressure to the wheel is maintained constant, or gradually increased with time.
2. Description of the Prior Art
A skid control system is used for a vehicle having at least one wheel and a brake for the wheel, by which skid control operation for the wheel is performed to avoid a locked wheel condition and obtain good braking performance on any road. In a conventional skid control system, rotational conditions of the wheel such as deceleration, slip and acceleration are measured to skid control the wheel. When the deceleration or slip of the wheel exceeds a predetermined threshold deceleration or a predetermined threshold slip, the brake pressure to the brake is decreased, and when the acceleration of the wheel exceeds a predetermined threshold acceleration, the brake pressure to the wheel is maintained constant, namely at the decreased brake pressure, or gradually increased.
A wheel speed sensor is associated with the wheel for detecting the rotational speed of the wheel. The acceleration, deceleration and slip of the wheel are measured on the basis of the detecting output of the wheel speed sensor. Known speed sensors include a rotating member fixed mounted in relation to the wheel and a stationary member affixed to the vehicle chassis. Wheel rotational velocity is determined by the relative rotational motion between these two members.
When vehicle braking forces are applied abruptly, a vehicle or, in particular, a motorcycle will rock forwardly about its center of gravity thereby momentarily reducing the relative rotational movement between the vehicle and its wheels. This results in an instantaneous and erroneous low wheel speed output from the wheel speed detector. Accordingly, the magnitude of the change of wheel speed detected by the wheel speed sensor is larger than that of the change of the actual wheel speed thereby decreasing the braking pressure more than required and unnecessarily lengthening the vehicle braking distance.